I think you mean you applied for S corporation status for the company to be effective starting in January of 2025, but you started doing business in December of 2024. Assuming you are a calendar year filer, you should not enter the December 2024 income and expenses on the 2025 S corporation tax return. Rather, you should report that income and expenses on the form for whatever tax entity you were before January of 2025, typically a sole-proprietorship, partnership or "C" corporation.